1. Field of the Invention
The present invention relates to an electronic part and a method of assembling the same. More particularly, the invention relates to an electronic part having therein a surface acoustic wave device or the like for use in a resonator and a frequency band filter of a portable telephone or the like and to a method of assembling the same.
2. Description of the Related Prior Art
An electronic device such as a surface acoustic wave device is conventionally mounted in a ceramic case or a metal case. For example, a ceramic case has a ceramic substrate on which an electronic device is mounted, some ring-shaped ceramic layers formed on the ceramic substrate, a metal ring in the uppermost layer, and a metal cap connected to the metal ring by a method of seam welding or the like. Since the electronic device and an external terminal of a bottom face of the ceramic substrate have to be electrically connected to each other, the ceramic layer has a wiring layer or internal wiring such as a through hole. A predetermined ceramic layer has a bonding pad which is connected to the internal wiring. The electronic device is connected to the bonding pad via a bonding wire. In the ceramic package, however, it is necessary to form the internal wiring and to stack ceramic layers. Each time the package size or wiring position is changed, a new mold for forming ceramic layers is needed. When the metal cap is sealed by seam welding, the metal ring has to be brazed on the ceramic layer. In the case of sealing the metal cap by solder, special solder is necessary. For the reasons, it is difficult to realize low cost of the electronic part.
As an example of an electronic part having a resin case which can be manufactured at low cost, Japanese Examined Utility Model Publication No. 56-015830 discloses an electronic part in which an insulating resin layer is formed on the outside of a surface acoustic wave device by a dip method and a conductive film is formed on the outside of the insulating resin layer. In the electronic part, expansion and contraction of the resin due to a change in outside temperature causes a change in characteristics of the surface acoustic wave device and a break in the bonding wire. Each of Japanese Patent Unexamined Publication Nos. Hei-05-063495 and Hei-06-188672 and Japanese Patent No. 2600689 discloses an electronic part in which a resin mold having a space is provided on a surface acoustic wave device or a semiconductor chip fixed on a metal lead frame. In the electronic part disclosed, the surface acoustic wave device or the semiconductor chip is directly mounted on the metal lead frame. With such a configuration, stray capacitances are generated and high frequency characteristics deteriorate. Each of the first and second literatures discloses an electronic part having an SIP (Single In-line Package) structure, that is, a configuration in which a lead extends linearly from one of the sides of the package. In the electronic part having the SIP structure, however, leads are concentrated on one of the sides of the package. Consequently, a tilt occurs when the electronic part is mounted on a printed board and an adverse influence is exerted on the characteristics of the electronic part.
It is therefore an object of the invention to provide a very reliable electronic part having small outer dimensions, and a method of manufacturing an electronic part by a simple assembling process with improved productivity at low cost.
An electronic part having a plastic package of the invention has: a resin base having a lead which is disposed from the top face to the outside of the plastic package; at least one electronic device mounted on the top face of the resin base; a conductor for connecting a lead portion on the top face of the resin base and the electronic device; and a resin cap which is bonded on the resin base so as to form a space between the resin cap and the resin base. In a specific example of the electronic part, the electronic device includes a surface acoustic wave device and is mounted in a recess in the top face of the resin base. The electronic device is disposed so that its electrode pattern forming surface faces the top face of the resin base via a space. At this time, the electrode pattern and the lead on the top face of the resin base are electrically connected to each other via a conductor. A part of the lead of the electronic part can be formed on a side face and/or a bottom face of the resin base. The whole lead which is on the outside of the plastic package can be formed on the surface of the plastic package. The lead is formed so as to extend from the top face of the resin base around the electronic device to an outer region of the resin base.
A method of assembling the electronic part has the steps of: forming a resin base by integrally molding a lead frame having a plurality of terminals and a resin so that a part of the lead frame is disposed from the top face of the resin base to the outside of the plastic package; mounting an electronic device on the top face of the integrally molded resin base; electrically connecting the electronic device mounted and a lead portion on the top face of the resin base; bonding a pre-molded resin cap and the resin base; and cutting a predetermined portion of the lead frame. The assembling method can further have a step of bending the lead portion extended from the plastic package along the surface of the plastic package.
According to the invention, a small, very reliable electronic part can be obtained by a simple process.